As an interior structure for a railway vehicle, an interior structure 800 shown in FIG. 11A that uses a reinforcement frame (referred to, hereinafter, as a “frame-type interior structure”) and an interior structure 900 shown in FIG. 11B in which a core member is stacked together with an inside panel and an aluminum plate (referred to, hereinafter, as a “sandwich-type interior structure”) are known. The above-described FIG. 11A and FIG. 11B show the interior structure at a door pocket (a side entrance of the railway vehicle that houses a door) where the highest stiffness is required. As shown in FIG. 11A, the frame-type interior structure 800 mainly includes a reinforcement frame 802 formed by a combination of metal-made rod members, and an inside panel 801 mounted on the reinforcement frame 802. The inside panel 801 is formed by stacking an aluminum layer, a melamine layer, and a sheet of paper on which a pattern is printed. The overall thickness of the inside panel 801 is about 1.4 mm to 1.6 mm. A portion indicated by reference symbol 803 in FIG. 11A is a body framing of a border between a side wall of a cabin and a ceiling (the same applies to a portion indicated by reference symbol 903 in FIG. 11B).
On the other hand, as shown in FIG. 11B, although the sandwich-type interior structure 900 does not include a reinforcement frame, the sandwich-type interior structure 900 includes, in addition to an inside panel 901a, a core member 901b mounted on the back surface of the inside panel 901a and having a thickness of 10 mm or more, and an aluminum plate 901c further mounted on the back surface of the core member 901b, all of which are bonded to each other by an adhesive. As the core member 901b, resin-based foam material including a vinyl chloride foam material and a urethane foam material, or a honeycomb material including paper honeycomb is used. A panel 901 in which the inside panel 901a, the core member 901b, and the aluminum plate 901c are stacked (referred to, hereinafter, as a “sandwich panel”) has a thickness of about 15 mm. Patent Literature 1 describes this sandwich panel.